The Portland City Council voted 5-0 during a raucous public meeting Wednesday morning to add fluoride to Portland's drinking water, ending the city's status as the only major U.S. city that hasn't approved fluoridation.

The unanimous decision -- affecting about 900,000 residents in Portland, Gresham, Tigard and Tualatin -- followed a nearly seven-hour hearing Sept. 6 in which people on both sides of the issue traded statistics and made impassioned pleas. Some argued that fluoride effectively fights tooth decay, for example, while others characterized fluoridation as forced medication.

Wednesday, the typically placid council chamber occasionally erupted in disorder. Mayor Sam Adams ejected several audience members and repeatedly reminded others to remain quiet. Some held anti-fluoride signs, booed and gave the elected officials a thumbs down. One protester unfurled a white sheet from a balcony. "Public water deserves a public vote," the homemade banner read.

Council members were undeterred. "This is the right thing to do, and I'm pleased to vote aye," said Commissioner Dan Saltzman, drawing jeers from the crowd.

Commissioner Amanda Fritz seemed to be the only one with misgivings, voting yes only after a lengthy prepared speech that revealed sympathy for opponents. Fritz is the only member who faces re-election in November. Her opponent, state Rep. Mary Nolan, had called on the council to back fluoride as an "equity" issue.

Adams and Commissioner Randy Leonard, who both decided not to seek re-election, leave office Dec. 31. Saltzman and Commissioner Nick Fish are in the middle of their terms.

Fluoride opponents vowed last month to launch an initiative to put the question of fluoridation to a public vote in May 2014. Then Leonard, the City Council's chief fluoride proponent, pledged to have fluoridation up and running March 2014.

Portlanders have voted against fluoridation three times, most recently in 1980. This time, opponents said they have 125 volunteers and expect to have 25 paid signature-gatherers. They declined to say how much money they expect to raise through their newly formed political-action committee, Clean Water Portland.

"This is not an issue for the faint of heart," Leonard reminded his colleagues during the vote.